Infrared thermopile type temperature sensors are well known. See, for example, U.S. Pat. No. 6,987,223 incorporated herein by this reference.
Calibration of individual infrared sensors involves aiming the infrared sensor at a black body held at a known temperature. The output of the sensor is then adjusted, typically be adjusting the calibration constants associated with the sensor electronics, until the sensor outputs the known temperature of the black body.
Calibrating such a package with dual sensors is problematic. Since the sensors are purposely aimed in different directions and since the black “calibration” body may have temperature variations across its surface, especially when the black body is fairly large in size to accommodate the field of views of both sensors, each sensor may detect a different temperature. Since the goal is that both sensors are to be calibrated to detect the same temperature, presently available calibration techniques and systems result in erroneous calibrations.